Re: Favourite Test Equipment

On 2024-04-05 11:31, John Larkin wrote:

On Fri, 5 Apr 2024 09:24:53 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
 

Jan Panteltje <alien@comet.invalid> wrote:
>

Giggle Hertz oscillations are not happening in LC circuits of specific
kind where those can happen you can figure from the parts used, no giggle
Hz in a BC109.

>
Back in the 1970s I found that a BC109 could be used as a self-
oscillating transmitter output stage at 100 Mc/s on a 1.5v supply (it
was for small animal cardiography).  Most "R.F." transistors wouldn't
work under those circumstances.

 I learned at an early age that emitter followers tend to oscillate. I
did a powerup reset circuit with an RC feeeding a 2N2219 emitter
follower feeding a TTL schmitt gate. The NPN oscillated at 100 MHz or
so and never pulled up the gate. A series gate resistor fixed it.
 My recent 50 MHz SAV541-based Colpitts oscillator couldn't be tamed
with a gate resistor or with a bead, so I gave up on the phemt. I
think the wire bonds are a basic hazard.
 https://www.dropbox.com/scl/fi/bak4p5bty2os2wtrs0091/9.jpg?rlkey=91e37ctc70189hvka9g1ufar3&raw=1
  

Try putting BLF03VK600 beads in source and drain. Besides being rated at 3 GHz instead of 100 MHz, it has really nice low Q everywhere.
My cascoded lab amp proto is using three SAV-331+'s in parallel like that, running about 2.5 mA each, and shows no sign of trouble.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com